My parents are planning a visit here in US in May,2018. I want to purchase roundtrip ticktets for them from KTM TO DC. My kids want to accompany them on the same return flight from DC TO KTM in June 2018, but I will have to do roundtrip ticketing for them,as they are returning in Sep2018. Can anyone share their experience on how to do this kind of same flight# ticketing ?